JavaScript Creational Design Patterns Factory with Composition
Example
'Prefer composition over inheritance' is an important and popular programming principle, used to assign behaviors to objects, as opposed to inheriting many often unneeded behaviors.
Behaviour factories
var speaker = function (state) {
var noise = state.noise || 'grunt';
return {
speak: function () {
console.log(state.name + ' says ' + noise);
}
};
};
var mover = function (state) {
return {
moveSlowly: function () {
console.log(state.name + ' is moving slowly');
},
moveQuickly: function () {
console.log(state.name + ' is moving quickly');
}
};
};
Object factories
6
var person = function (name, age) {
var state = {
name: name,
age: age,
noise: 'Hello'
};
return Object.assign( // Merge our 'behaviour' objects
{},
speaker(state),
mover(state)
);
};
var rabbit = function (name, colour) {
var state = {
name: name,
colour: colour
};
return Object.assign(
{},
mover(state)
);
};
Usage
var fred = person('Fred', 42);
fred.speak(); // outputs: Fred says Hello
fred.moveSlowly(); // outputs: Fred is moving slowly
var snowy = rabbit('Snowy', 'white');
snowy.moveSlowly(); // outputs: Snowy is moving slowly
snowy.moveQuickly(); // outputs: Snowy is moving quickly
snowy.speak(); // ERROR: snowy.speak is not a function
